Conventional exhaust sensors, better known as oxygen sensors, have been utilized to monitor the exhaust from combustion engines such as those in automotive vehicles. Primarily, these oxygen sensors have been used to monitor the equilibrated oxygen content in the combustion exhaust for the purposes of controlling the fuel-to-air ratio delivered to the combustion engine so the combustion occurs at stoichiometric conditions. Such oxygen sensors utilize platinum electrodes which have a catalytic affect on the exhaust constituents passing through the electrode. Consequently, platinum electrode exhaust sensors do not accurately measure the actual constituents in the exhaust gas. They do, however, measure the equilibrium oxygen content. While systems that use a conventional oxygen sensor placed after the converter to diagnose how well the converter is performing have been developed, these suffer from the disadvantage that the sensor is not sensitive to the actual regulated constituents that define the performance of the converter.
The present invention overcomes many of the disadvantages of the prior art.